1. Field of the Invention
This invention relates to a media access control for handling transmission and reception of isochronous data and asynchronous data. More particularly, the invention relates to preventing collisions during the transmission of isochronous data in carrier sensing multiple access transmission systems.
2. Description of Related Art
With the advent of multimedia processing in computing systems and increased deployment of digital audio and video formats, there is an increased demand for reliable transmission of synchronous and isochronous data over standard computer networks. Audio and video are but examples of synchronous or isochronous data. Any data stream that must be clocked and continuous would be considered synchronous. A data stream which must be delivered with determinant latency could be considered isochronous.
Local area networks, such as Ethernet, were developed to carry computer data. Computer data is primarily asynchronous in nature, and is not highly sensitive to non-deterministic latencies. Ethernet uses a carrier sense multiple access with collision detection media access control protocol (CSMA/CD MAC). This type of MAC is characterized by very low typical latencies, and reasonably high potential throughput.
The shortcomings of Ethernet for the transmission of synchronous and isochronous data are in it's potentially high latencies when collisions occur between stations transmitting on the network. Numerous schemes have been developed for the transmission of synchronous and isochronous data over multiple access transmission systems. A reservation system typically employs two communications channels; one channel, the reservation channel, is used to communicate reservation requests from individual stations to a central authority which then allocates bandwidth in the primary channel, as requested, if possible. The reservation channel typically carries asynchronous data, while the primary channel carries isochronous data. Several schemes have been previously devised to implement a reservation system on a single multiple access channel. These schemes involve time dividing the channel into "frames" and further subdividing the frames to create the two channels required for a reservation system. One such system divides a frame into two Time Division Multiplexed (TDM) regions, one for the primary channel and one for the reservation channel. Another scheme splits frames into a TDM primary channel region and a CSMA reservation region. To date, there is no solution to collision problems in a CSMA protocol without significant inefficiencies in transmission.